We have one God(I Am, Deut 6:4), but He is a God that has particularly manifested HIMSELF to the world in three manners(father in creation, the Son in redemption, Holy Spirit operating in the church and in the world today).
The concept of the trinity explains to many, and including myself that HE has three different personalities as well as being three different persons. This is what is taught and has been believed for hundreds upon hundreds of years.
Now, even many of the Nicean council members of 324-326 ad argued and debated extensively, and a trinitarian God was not accepted. Trintarian God was embraced and accepted by Constantine and many catholics and sects of that day. This can be extensively researched by any one interested in more facts.
I will say this that when I have spoken to trinitarians on this issue, and it gets explained to them in the manner in which the Yewish woman explained it too me, then they respond " oH yeh, that's right, or thats what I meant"...
Lastly, this is not and shouldn't be a doctrine or issue of division, I believe the revelation of who Yeshua(YHWH saves) is must come from a direct heavenly understanding and not our own or it will continue or forever be a mystery.
for as the great apostle stated in I Timothy 3:16," great is the mystery of Godliness", for God was manifested in the flesh. How wonderful this is to know and have communicated to we meager creatures? God is soooo good!
The Yewish person understands that there is only ONE God with one personality that is revealed and communicated by HIMSELF to the world through HIS son and through the Holy Spirit. Note: I will not make this a doctrinal issue of argument, I AM JUST RESPONDING TO YOUR REQUEST OF EXPLANATION AS BEST AS I CAN THROUGH WHAT GOD HAS SHOWN US....
Blessings, Honour and Power be unto God